Other civilisations in the Galaxy - are they really that likely?

I have always been fairly conservative (dismissive even) regarding the possibility of other "intelligent" life in the universe. This comes from gut feeling, aesthetics(!) and the Fermi paradox. Now it's time to get scientific with the issue, as there seems to be a good number of experts around here in the relevant fields. I'm looking at a sort of "informed" Drake Equation...By stipulating Galaxy, I'm just giving us a working number of star systems. I'm quite happy for this to branch out to the observable universe once we have a handle on the numbers.My opening comments...What's the earliest opportunity for a suitable planet to form?What conditions do we really need for abiogenesis?How long do we need to wait for abiogenesis? (~1Gyr in our case)How long for progress beyond prokaryote stage? (~2Gyr in our case)Now, where to put it? Origin of Life?

Thread moved here from the Proposed New Topics forum.

quote:

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N = R* x f_p x n_e x f_l x f_i x f_c x L

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where:

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N is the number of extraterrestrial civilizations in our galaxy with which we might expect to be able to communicate

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and

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R* is the rate of star formation in our galaxy
f_p is the fraction of those stars which have planets
n_e is average number of planets which can potentially support life per star that has planets
f_l is the fraction of the above which actually go on to develop life
f_i is the fraction of the above which actually go on to develop intelligent life
f_c is the fraction of the above which are willing and able to communicate
L is the expected lifetime of such a civilization

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Drake equation - Wikipediain high school i tried plugging various estimates into the equation, and managed to get results ranging from "we're the only intelligent lifeforms in the galaxy and we're damned lucky to be here" to "second star to the right and straight on til morning and you'll find a few"

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אָרַח

Hey, cavediver, I'm a big fan of Fermi's paradox. I tend to be skeptical that advanced civilizations are very common in the galaxy.One nit-pick though:

quote:

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How long do we need to wait for abiogenesis? (~1Gyr in our case)

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If the 1 Gyr refers to the time from the very beginning of the solar system to the first signs of life, then this is accurate, I believe.However, it is a little misleading. It seems that this is also about the time of the end of the heavy bombardment, during which life would be impossible. So it seems that life appears immediately (geologically speaking, of course) once conditions allow for it.Unless our solar system is rare in that the heavy bombardment eventually ceased -- then this example does become relevant.On the other hand, I, too, have noticed how long it took for prokaryotic and more advanced life to come about. Perhaps complex multicellular life is pretty rare.Ah, the unknowns! It is very hard to get reliable statistics out of a single data point.

Not a very good attitude to go at such a question. Yes, I'm sure an equation based on one single data point is such an important break through Huh? They're working on it right now, but from what we have discovered so far it would seem that amino acids, proteins, strands of RNA, and other organic compounds have a relatively high probability of forming by themselves if conditions are in favor.My take on it?From what we have gathered, it is very likely for life to have formed elsewhere. However, for life to evolve to a stage where intelligence and ingenuity is at a level sophisticated enough to build a civilization is another story. Intelligence alone is also very likely. There are many creatures on Earth other than man that are extremely intelligent. However, we seem to be the only species that have the capacity to build civilizations that survived the evolutionary process.If, on the other hand, we share this planet with another species that is capable of building their own civilizations (like the Xindi), then I would say that there are more chances for other civilizations to exist out there than now.

The gut feeling that *I* have always had, is that the Fermi-paradox might not be a paradox at all, because civilizations might never reach a situation where they take the necessary steps to "colonize" their galaxy. I don't even mean that in the sense that they destroy themselves or get destroyed by the multitude of available mass-extinction events (although those also make sense...). It's also simply a matter of the difference between the "possible" and the "actual". It is not enough that something is theoretically, or technically, or socially, or even economically possible, for it to actually materialize. You just have to look around to see examples of that all the time.So I think it's pretty likely that there have been millions of intelligent civilizations in the universe, and none (or very few) of them have had the capability to get in touch, "live" or just via communication.In any case, with just one data-point this whole issue will remain (interesting) speculation for a long time to come

Not necessarily. If there have been indeed millions of intelligent civilizations capable of technology, then we would expect the galaxy to be filled with radio signals. Just look at us. We have been broadcasting radio signals for the last 50+ years.

So far we have only examined one form of life. And we've really only looked at one form of technology that would produce what you describe.Is there any reason to think that other life might be entirely different and that technology too might be different?

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Aslan is not a Tame Lion

Before long, we shall be doing most of our communication with cable, fiber, or low powered radio links, none of which would be observable by civilization on other inhabited planets. That leaves earth as potentially visible for only 100 years out of 500M years. That seems like a low visibility ratio.

Yes, and that is why I suspect that IFF there are other civilizations out there and that some are or will be advance enough to breach the barriers between their worlds, mainly vast distances of space, there would likely be wars as a result of misunderstanding of each others' notions of what's intelligence and what's advance. Ender's Game presents a very good example of that.

If abiogenesis turns out to be just the right mix of chemicals and conditions, no reason why, in the multiplicity of similar planets, similar chems/conditions couldn`t take place.
With evidence from Mars pointing to the presence of water, will discovery of life (fossilised or active)prove the death-knell for Christianity? Not so, say the creos, God inspired His Bible purely for Earthlings. The Martians had another Bible.

Not at all, but that would probably do better in its own thread.

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Aslan is not a Tame Lion

It is my considered opinion that however different the life form the technologies will converge as they advance. (Digney's 4th law of exosociology)Here is why:A species that is enormously different than ours perhaps that has a radio sense but much more limited sight than ours (living on a permanently foggy world?) might match Marconi at a point in their civilization equivalent to the Roman Empire in ours.In other words, we and they pick off the technologies that are both more suited to us and easiest. By easiest I might mean simple mechanical tools or engines over nuclear power and solid state devices.However, as we both advance into more difficult areas what we both know would be more and more overlapping.At some point a race that is say, more into the biological sciences will start to explore nuclear physics and one like ours will beging to advance in the biological area. After a century of this we are both in possession of about the same technologies.

I agree and would think there should be more radio signals if the galaxy was filled with intelligent civilizations, (i.e. at or above our level of technology).OTOH, our signals have only ventured out 50 light years. Considering the galaxy diameter at approximately 100,000 light years, then our signals have not traveled very far at all. Considering the time for a return signal, then only civilizations within a 25 light year envelope would have had a chance to return the call such that we could now hear them.This, of course, assumes: 1)They want to answer, 2)their technology is sufficiently advanced to pick up our puny signal strength, 3)they developed radio technology in the first place, 4)are currently using it, and 5)are looking at the right frequency/direction. Then on the return call, we would need to be looking at the right frequency/direction. That's a lot of "ifs". There may be many, (millions?) out there, it's just that all favorable conditions for contact have not been met.Given all of these "if's", I think it much more likely that if we detect a signal it will be an accident and a signal that is not intended specifically for us.

Reasonable. But what we're counting on is a small segment of that technology, using broadcast radio. Any other technology, such as narrow casting, advances in landline communications as an example, where the broadcast stage is minimized or skipped, would make it almost impossible for us to detect them.

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Aslan is not a Tame Lion